The invention relates to the field of chemical lasers and, more particularly, to a gain generator for use in high-energy flowing gas chemical lasers.
The chemical oxygen-iodine laser (COIL) is a high-energy chemically pumped continuous wave (cw) laser which utilizes electronic transitions between different states of atomic iodine. The COIL can produce continuous high-power and good beam quality due to low pressure operation.
The overall process in the COIL involves the liquid phase generation and flow of electronically excited molecular, singlet-delta oxygen, O.sub.2 (.sup.1 .DELTA.), into the gaseous phase. This is followed by electronic energy transfer to metastable atomic iodine to produce the excited state of atomic iodine. O.sub.2 (.sup.1 .DELTA.) is generated by a chemical reaction between basic hydrogen peroxide (BHP), HO.sub.2 -, and chlorine gas, Cl.sub.2. Resonant energy transfer from O.sub.2 (.sup.1 .DELTA.) produces excited state atomic iodine I(P.sub.1/2) and a population inversion: EQU O.sub.2 (.sup.1 .DELTA.)+I(P.sub.3/2).fwdarw.O.sub.2 (.sup.3 .SIGMA.)+I(P.sub.1/2) (1)
The ground state iodine atoms for reaction (1) can be produced by the dissociation of molecular iodine, I.sub.2, introduced into a flow stream of O.sub.2 (.sup.1 .DELTA.). The transition between the first electronically excited state of atomic iodine and the ground state generates a photon at 1.315 .mu.m: EQU I(P.sub.1/2).fwdarw.I(P.sub.3/2)+h.nu.(1.315 .mu.m) (2)
Lightweight versions of high-energy chemical lasers are emerging strategic weapons having potential for airborne use. In the gain generator, a resonant transfer of energy occurs through the reaction of the energizing reactant, O.sub.2 (.sup.1 .DELTA.), and the lasing reactant, iodine. Lightweight materials are needed in the gain generator for airborne applications where weight reduction reduces fuel consumption and operating costs.
The materials used in the gain generator also need to have resistance to high-temperature chemical attack by aggressive chemicals. In the COIL, the nozzle blades need to be chemically resistant to iodine and also to residual chlorine (Cl.sub.2) from O.sub.2 (.sup.1 .DELTA.) generation.
Materials used to form the nozzle blades in COIL devices also need to have sufficient mechanical properties at operating temperatures typically as high as 300.degree.-400.degree. F. Strength is needed to maintain acceptable dimensional stability of the nozzle.
Known metallic nozzle materials such as high-purity nickel and nickel-based alloys must be heated to a temperature above about 400.degree. F. to prevent I.sub.2 condensation on the blades, which can reduce I.sub.2 flow. Consequently, a heating source must be included in the gain generator to heat the nozzle blades.
These metallic materials are also difficult and expensive to cast and machine.
A further need for the nozzle blade material is that it does not catalyze the deactivation of O.sub.2 (.sup.1 .DELTA.). Deactivation reduces the amount of O.sub.2 (.sup.1 .DELTA.) available in the nozzle for electronic energy transfer to iodine and, thus, reduces photon output.
Another problem encountered in COIL devices is efficiently extracting power from the gain medium while at least satisfactorily matching the laser beam director geometry. In high-energy flowing gas chemical lasers such as COIL devices, it is often advantageous to use a laser beam director with circular optics. Due to diffraction effects, power at the target is increased by filling this aperture as much as possible. High-energy laser gain mediums are typically trapezoidal in shape, however, with a narrower dimension at the nozzle exit plane. Furthermore, the laser power is commonly extracted using an optical resonator which requires that the laser mode have an inversion symmetry about its optical axis.
Known solutions to this problem include either using a rectangular beam and physically clipping the corners after out coupling, or using a circular or elliptical extraction beam. These solutions are less than totally satisfactory. Clipping the corners of a rectangular beam after extraction sacrifices the outcoupled power that is clipped. Furthermore, in laser resonators with inversion symmetry, the rectangle height must be selected to match the shorter width dimension of the gain medium near the nozzle outlet end.
Using a circular or elliptical extraction geometry is also less than totally satisfactory. These geometries are more difficult to fabricate. Also, in transfer lasers such as the COIL, these geometries are less efficient and more sensitive to intensity spikes at the top and bottom.
Thus, there is a need for a gain generator for use in high-energy chemical lasers such as chemical oxygen-iodine lasers that (a) is lightweight; (b) comprises a nozzle that (i) is resistant to high temperature chemical attack, (ii) has sufficient mechanical properties at high temperatures, (iii) includes blades that are easier and less expensive to manufacture than metallic blades, do not require heating by a separate heating source, and do not catalyze deactivation of chemical reactants; and (c) provides both increased power extraction efficiency from the gain medium and satisfactory matching of the laser beam director geometry.